The typical structure and operation of positive-displacement machines of the spiral type are known for instance from German Patent Disclosure DE-C3-2 603 462. A compressor designed on this principle is distinguished by virtually pulsation-free feeding of the gaseous operating medium, which comprises air or an air-fuel mixture, for instance, and could therefore advantageously be used for supercharging internal combustion engines, among other purposes. During operation of this kind of compressor, a plurality of approximately crescent-shaped work chambers are enclosed along the positive displacement chamber between the spiral positive displacement body and the two peripheral walls of the positive displacement chamber; as these crescent-shaped work chambers move from the inlet through the positive displacement toward the outlet, their volume decreases continuously and the pressure of the operating medium increases accordingly.
A machine of the type described at the outset is known from European Patent Disclosure EP 0 354 342. In that machine, and in all the other known spiral compressors, in which a guide shaft operating in angular synchronism with the drive shaft is provided for the sake of translational guidance of the rotor, the bearing of the drive shaft is achieved with roller bearings. This can be seen especially clearly in the positive-displacement machine of EP 0 354 342, in which the drive shaft is supported in the housing in two ball bearings, and the eccentric collar disposed on the drive shaft is supported via a needle bearing.
This type of support of the rotor on the eccentric disk, because of the heavy centrifugal load and the eccentric motion, requires oil lubrication of the eccentric bearing, the oil being delivered to the bearing via a system of bores in the drive shaft. One such bore system is described in German Patent Disclosure DE 33 20 086 A1.